FLIGHT International supplement, 23 September 1965 Air-Cushion Vehicles
Background to Skirts, Fans
and Annular Jets
MORE HISTORICAL RESEARCHES
SHADOW boxing, sparring matches—
slogging matches even—could hardly be
absent from such a new and beckoning
industry as that which concerns this
journal. To us in Britain the legal
situation is, and will continue to be, a
prickly one in a domestic sense, and
acutely awkward, perhaps, when viewed
internationally.
One comforting aspect is that Chris-
topher Cockerell and his associates
appear to have done a thorough job in
patenting the various schemes and
devices which they have proposed,
brought to reality, and in some instances
raised to commercial pitch.
The innermost factors in the threat-
ened litigation (whatever form it may
take) are screened from public view,
and the last reference made to the sub-
ject in these pages was over a year ago.
It was then recorded that during the
months to come the US Patent Office
would be taking testimony from two
^American claimants—Mr Melville
Beardsley and Dr William Bertelsen—
to the invention of what is popularly
known in England as the "hovercraft."
The Cockerell patents covered not
only the sealing of the air cushion by a
curtain of air ejected downward and
inward around the periphery of the craft,
but mention was also made of flexible
extensions, in token of the inventor's
dictum that the ideal hovercraft should
be "as flexible as a jellyfish and as light
as a pocket-handkerchief."
Meanwhile, C. H. Latimer-Needham
obtained a patent in 1959 relating (I
quote Westland's patent manager) to the
provision of flexible skirts adaptable to
any form of ground-effect machine to
maintain the air cushion at a consider-
able depth, thereby giving a greater
clearance height in operation. This
patent was acquired by Westland, with
the result (I quote Westland them-
selves) that the Hovercraft became some-
thing more than the "interesting idea"
which "almost certainly" it would have
remained.
Other makers have adopted and
adapted the skirt, and such is its impor-
tance in ACV technique that it may
come to many people in the industry as
something of a surprise—if not as a
shock—to learn that the essence of the
idea is well over half-a-century old.
In Patent No 17,525 of 1909, Hans
Peter Dinesen, civil engineer, of Frid-
hem, near Malmo, Sweden, declared his
invention to be "particularly described
and ascertained in and by the following
statement":—
The relevant figures
from Dinesen's patent
"The resistance opposed to a ship in its
advance through water, is constituted by the
following resistance elements: frictional resis-
tance between the water and the immersed
outer skin advancing through the same, and
displacement resistance, that is to say, the
counter pressure which water offers to the ship
as it displaces it during its advance movement,
the said displacement resistance depending on
the form of the ship, the immersed portion and
the midship section as well as on the speed. The
latter kind of resistance embraces also the eddy
and wave resistance due to the movements of
water accompanying the displacement of
water.
"In addition to the above mentioned resis-
tances, there are also resistances and losses
which are due to the propelling means. The
screw propeller reduces for instance the pres-
sure of the water on the stern end of the ship,
and in addition to that, imparts a certain
rotary motion to the water against which it
acts, which results in a considerable loss of
energy.
"This invention has for its object generally
to reduce the resistance offered to the ship, on
the one hand, by reducing the single resistances
themselves, and on the other hand, by forcing
certain resistances to act in opposition to each
other, and to thus become completely, or
partly, neutralized. This is effected, firstly, by
utilizing the means suggested by De Laval [it
had, in fact, been employed in public service
decades before] for reducing the frictional
resistance, consisting in converting a surface
in contact with water, into a surface in contact
with air, but in a manner which attains the
object in question more satisfactorily, and
secondly, by reducing displacement resistance,
and further also by utilizing the movement of
water which brings about a loss in the case of
upward or forward propelling forces, for
reducing the portion of the propelling power
or energy utilized for overcoming the
displacement resistance.
"The invention comprises a ship with air-
chamber underneath the bottom, character-
ized by the fact that the centre of gravity of the
ship is so arranged in relation to the resultant
of the forces tending to effect the buoyancy,
that the lowermost edge of the foremost end
wall of the air-chamber during the movement
of the ship is level with the exterior water
surface while simultaneously the lowermost
edge of the aftermost end wall of the air-
chamber is substantially level with the water
surface in the air-chamber immediately in
front of the last mentioned innermost edge."
Later Dinesen declared:—
"In case of smaller ships and in a heavy sea,
it may happen that the fore part of the ship
would come out above the water surface, so
that the air from the chamber 14 could escape
between the oblique surface and the water. A
portion of the surface can, therefore, be con-
structed as one or more adjustable or pivoted
plates, so that its edge always follows the
water surface and thus prevents the air from
escaping. In Figure 31a portion of the surface
15 is made as a plate of rubber [my italics] or
some other elastic material connected to the
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